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16 Cards in this Set

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becker/duchene muscular dystrophy: sympotoms, cause, inheritance type

BMD is milder characterized by later onset of skeletal muscle weakness; both are caused by mutations in the Dystrophin gene which encodes a component of the cytoskeleton in myocytes (lnikes the actin to the membrane so more movement=more damage); primarily affects males but females may be affected too; X linked recessive condition; allelic heterogeneity; Gower's maneuver; the dystrophin gene is located on chromosome Xp21; largest gene in the human genome; most cases of DMD and BMD are caused by deletions within the gene; severity of the dystrophy is primarily associated with whether a deletion maintains the protein reading frame or not

lesch nyan syndrome: symptoms, cause, inheritance type

multisystem disorder with most prominent features in neural tissue; individuals with LNS appear normal at birth and for 1st few months; later symptoms include self mutilation and spasticity of the limbs; LNS is caused by mutations in the HPRT1 (aka hyposanthine guanine phosphoribosyl transferase (HGPRT)) gene which is located at Xq26-q27.2; allelic heterogeneuty= more than 200 independent mutations detected in HPRT1; mutations that severely decrease HGPRT activity cause LNS, less severe mutations cause gouty arthritis (aka kelley seegmiller syndrome); HPRT1 catalyzes the salvage of purine bases (hypoxanthine and guanine) by joining them with phosphoribosyl pyrophosphate (PRPP); gouty arthritis is caused by accumulation of uric acid in serum and in joint fluids; the neurological effects of HPRT1 deficiency are caused by a lack of purine nucleotides and possibly also by defects in neurotransmitter synthesis; X linked recessive

rett syndrome: symptoms, cause, inheritance type

most cases caused by mutations in the methyl CpG binding protein 2 (MECP2) gene at Xq28; a small number of cases have been associated with mutations in the FOXG1 gene at 14q13 (example of LOCUS HETEROGENEITY); it is characterized by arrested development between 6 and 18 months of age, regression of acquired skills, loss of speech, stereotypical movements (classically ringing of the hands), microcephaly, seizures, and mental retardation; rarely seen in males (possibly associated with additional genetic anomalies such as presence of additional X chromosome); X linked dominant

locus heterogeneity definition

2 different genes mutated with same effect

turner syndrome: symptoms, cause, inheritance

webbed neck, edema of hands and feet (related to coarctation of the aorta), low birth weight, shield like chest, renal abnormalities, gonadal dysgenesis, short height; this is due to inheriting only 1 X; monoploidy; may be genetic mosaics

klinefelter syndrome: symptoms, cause, inheritance

small external genitalia, long legs, behavioral disorders, gynecomastia, tall height, infertile; this is due to inheriting XXY

penta X syndrome

5 X chromosomes; due to nondisjunction in BOTH meiosis I and II and then of course fertilization

how can someone like this be alive? the Xs are big and code for a bunch of stuff

X chromosome inactivation; the inactivated one becomes a barr body that is dark and heterochromatic; this means that in both males and females there is only ever ONE X chromosome active

what is an exception to this

there is a region on the inactivated X chromosome called the pseudoautosomal region (PAR) that IS NOT inactivated (obvi why it is called pseudoautosomal); one of the genes in this region is the SHOX gene (aka short stature homeobox gene) so this is why you see short stature in Turner syndrome and the tall stature in Klinefelter syndrome


the sex determining region on the Y chromosome; this region is very close to the PAR region on the Y chromosome and the PAR region can pair and recombine with its paired X chromosome PAR region (the X and Y pair for meiosis and this is where they pair); because of the possible recombination it could slip up and take the SRY region with it (from the normal Y position to the abnormal X position) and this can lead to sex reversal (mutations in SRY can also result in sex reversal)

conclusions: males inherit X linked recessive disorders from

a carrier mother

conclusions: fathers pass X linked dominant disorders to

all their daughters

conclusions: DMD (representative X linked recessive disorder) displays what heterogeneity

allelic resulting in variation of severity of disorder

conclusions: turner and kleinfelter syndromes represent

chromosomal disorders due to monosomy or functional trisomy of sex chromosomes

conclusions: X chromsome inactivation is a mechanism for achieving

dosage compensation between the sexes

conclusions: the X and Y chromosomes contain what region

a homologous region (the pseudoautosomal region or PAR) which escapes X chromosome inactivation